Auditing Technical SEO
Overview
Technical SEO is the foundation. Content strategy, keyword work, and link building all assume that Google, Bing, and AI-search crawlers can actually fetch, render, and trust your pages. If any of those fail, nothing else compounds. In 2026 that surface is wider than it used to be: Core Web Vitals are still the user-experience signal Google measures at the 75th percentile with thresholds LCP < 2.5s, INP < 200ms, CLS < 0.1 [1], and a new tier of AI crawlers — GPTBot, ClaudeBot, Claude-SearchBot, PerplexityBot, Google-Extended, Applebot-Extended — now decides whether your content shows up in ChatGPT, Claude, and Perplexity answers [2][3].
What this skill checks
- Crawlability:
robots.txt parses cleanly, no accidental site-wide Disallow: /, sitemap referenced as absolute URL, sitemap reachable and valid, file under 500 KiB (Google's hard cap) [6][7].
- Indexability: GSC index coverage cross-referenced via
gsc-mcp, canonical tags consistent and self-referential where appropriate, hreflang correct on i18n sites, no duplicate content via tracking parameters, no noindex on pages that should rank [5].
- Rendering: SSR/SSG vs CSR-only routes (CSR-only pages are largely invisible to GPTBot/ClaudeBot/PerplexityBot, which do not execute JS reliably), critical content not hidden behind hydration [2][3].
- Core Web Vitals: LCP, INP, CLS, TTFB measured at p75 via
lighthouse-mcp (PageSpeed Insights / CrUX field data) [1].
- Schema: JSON-LD present in
<head> or root layout, types valid against schema.org (Article, BlogPosting, Organization, FAQPage, BreadcrumbList, Product as appropriate), validates via validator.schema.org [4].
- AI-search readiness:
robots.txt makes a deliberate choice on GPTBot, ClaudeBot, Claude-SearchBot, PerplexityBot, Google-Extended (allow or block — both are valid; absence is the bug) [2][3]. llms.txt presence noted but not required: adoption is ~10% of domains and effect on AI citations is unproven [8].
- Mobile: viewport meta present, mobile-friendly via PSI mobile run.
- Security: HTTPS only, HSTS header, no mixed content, valid certificate.
- Meta basics: unique
<title> (50–60 chars) and meta description (150–160 chars) per page; Lighthouse SEO category flags these explicitly [5].
The audit flow
1. Gather. Read repo files: package.json (framework detection), app/robots.ts or public/robots.txt, app/sitemap.ts or public/sitemap.xml, app/layout.tsx (or Astro Layout.astro / SvelteKit +layout.svelte) for <head> schema, next.config.js / astro.config.mjs / svelte.config.js for redirect/rewrite rules. Then fetch the live site's /robots.txt, /sitemap.xml, /llms.txt. Call lighthouse-mcp for PSI on the homepage and 2–3 representative inner pages (mobile + desktop). Call gsc-mcp if connected for index coverage and submitted-sitemap status.
2. Cross-reference. Does the deployed sitemap match what GSC has on file? Are CSR-only routes leaking into the sitemap? Does robots.txt block any URL that's also in the sitemap (the classic conflict) [7]? Are GSC-reported "Discovered – currently not indexed" URLs concentrated in one route group?
3. Write SEO_AUDIT.md to repo root. Findings ranked by traffic-impact × fix-effort in a quadrant — high-impact / low-effort first.
4. Open ONE PR with the highest-confidence, low-risk fixes only: adding viewport meta, adding missing meta descriptions, adding Sitemap: line to robots.txt, adding explicit GPTBot/ClaudeBot allow-or-block stanza, adding root Organization JSON-LD. Leave architectural calls (CSR → SSR migration, image pipeline rework) for human decision in the audit doc.
Output format — SEO_AUDIT.md shape
# SEO Audit — example.com — 2026-04-26
## Quadrant
LOW EFFORT HIGH EFFORT
HIGH IMPACT | Add meta descriptions | Migrate /blog to SSR
LOW IMPACT | Tidy llms.txt | Refactor schema graph
## Findings
### [P0] Sitemap not referenced in robots.txt
Severity: high · Effort: 5 min · Confidence: 100%
Fix: Add `Sitemap: https://example.com/sitemap.xml` to `app/robots.ts`.
### [P0] LCP 4.1s on /pricing (p75 mobile)
Severity: high · Effort: medium · Confidence: 90%
Cause: hero image not preloaded, no priority hint.
Fix: <Image priority fetchPriority="high" /> on hero.
### [P1] No GPTBot/ClaudeBot stanza in robots.txt
Severity: medium · Effort: 2 min · Confidence: 100%
Decision required: allow or block? Both are valid choices.
Lifecycle awareness
Mirroring the lifecycle pattern in finding-underserved-keywords:
- Initial (pre-launch / first 3 months): focus on indexability, schema, sitemap correctness, canonical hygiene, robots.txt sanity. Core Web Vitals data isn't statistically meaningful yet — CrUX needs traffic.
- Growth (3–12 months): add CWV regressions and mobile-friendliness; cross-reference GSC index coverage to catch routes silently dropping out.
- Mature (12+ months): decay defense — schema drift (types deprecated upstream at schema.org), CWV regressions from third-party script creep, sitemap bloat from old URLs, AI-crawler policy review as new bots emerge.
Common mistakes
- Running the audit before the site is deployed — most checks need a live URL.
- Conflating crawlability with rankings — fixing robots.txt won't lift a thin-content page.
- Skipping mobile — Google indexes mobile-first; desktop-only Lighthouse misses real failures.
- Blocking AI-search bots without realizing — broad
Disallow: / against User-agent: * blocks ClaudeBot too [3].
- Treating Lighthouse SEO score as the audit — it's 8 pass/fail checks, not a strategy [5].
Common false positives
- Lighthouse flagging "image elements do not have explicit width and height" on the LCP image when it's intentionally the hero — that's correct architecture, not a bug.
- Schema.org validator "warnings" that are recommendations, not errors — distinguish before opening a PR.
- PSI showing CWV "needs improvement" on a brand-new page — CrUX field data is sparse; lab data only at this stage.
llms.txt missing — flag as suggestion only; no measurable AI-citation effect yet [8].
Citations and verification tags in SOURCES.md.
1---2name: auditing-technical-seo3description: Use when running a technical SEO audit, debugging Core Web Vitals regressions, checking indexability, validating schema and sitemaps, diagnosing why a site isn't ranking, or preparing a site for AI-search visibility (GPTBot, ClaudeBot, PerplexityBot). Covers crawlability, indexability, rendering, Core Web Vitals, schema, AI-search readiness, mobile, security, and meta basics. Lifecycle-aware — pre-launch, growth, mature. Produces a prioritized SEO_AUDIT.md and a low-risk fix PR.4---5
6# Auditing Technical SEO
7
8## Overview
9
10Technical SEO is the foundation. Content strategy, keyword work, and link building all assume that Google, Bing, and AI-search crawlers can actually fetch, render, and trust your pages. If any of those fail, nothing else compounds. In 2026 that surface is wider than it used to be: Core Web Vitals are still the user-experience signal Google measures at the **75th percentile** with thresholds **LCP < 2.5s, INP < 200ms, CLS < 0.1** [1], and a new tier of AI crawlers — GPTBot, ClaudeBot, Claude-SearchBot, PerplexityBot, Google-Extended, Applebot-Extended — now decides whether your content shows up in ChatGPT, Claude, and Perplexity answers [2][3].
11
12## What this skill checks
13
14- **Crawlability:** `robots.txt` parses cleanly, no accidental site-wide `Disallow: /`, sitemap referenced as absolute URL, sitemap reachable and valid, file under 500 KiB (Google's hard cap) [6][7].
15- **Indexability:** GSC index coverage cross-referenced via `gsc-mcp`, canonical tags consistent and self-referential where appropriate, hreflang correct on i18n sites, no duplicate content via tracking parameters, no `noindex` on pages that should rank [5].
16- **Rendering:** SSR/SSG vs CSR-only routes (CSR-only pages are largely invisible to GPTBot/ClaudeBot/PerplexityBot, which do not execute JS reliably), critical content not hidden behind hydration [2][3].
17- **Core Web Vitals:** LCP, INP, CLS, TTFB measured at p75 via `lighthouse-mcp` (PageSpeed Insights / CrUX field data) [1].
18- **Schema:** JSON-LD present in `<head>` or root layout, types valid against schema.org (Article, BlogPosting, Organization, FAQPage, BreadcrumbList, Product as appropriate), validates via `validator.schema.org` [4].
19- **AI-search readiness:** `robots.txt` makes a deliberate choice on GPTBot, ClaudeBot, Claude-SearchBot, PerplexityBot, Google-Extended (allow or block — both are valid; absence is the bug) [2][3]. `llms.txt` presence noted but not required: adoption is ~10% of domains and effect on AI citations is unproven [8].
20- **Mobile:** viewport meta present, mobile-friendly via PSI mobile run.
21- **Security:** HTTPS only, HSTS header, no mixed content, valid certificate.
22- **Meta basics:** unique `<title>` (50–60 chars) and `meta description` (150–160 chars) per page; Lighthouse SEO category flags these explicitly [5].
23
24## The audit flow
25
26**1. Gather.** Read repo files: `package.json` (framework detection), `app/robots.ts` or `public/robots.txt`, `app/sitemap.ts` or `public/sitemap.xml`, `app/layout.tsx` (or Astro `Layout.astro` / SvelteKit `+layout.svelte`) for `<head>` schema, `next.config.js` / `astro.config.mjs` / `svelte.config.js` for redirect/rewrite rules. Then fetch the live site's `/robots.txt`, `/sitemap.xml`, `/llms.txt`. Call `lighthouse-mcp` for PSI on the homepage and 2–3 representative inner pages (mobile + desktop). Call `gsc-mcp` if connected for index coverage and submitted-sitemap status.
27
28**2. Cross-reference.** Does the deployed sitemap match what GSC has on file? Are CSR-only routes leaking into the sitemap? Does `robots.txt` block any URL that's also in the sitemap (the classic conflict) [7]? Are GSC-reported "Discovered – currently not indexed" URLs concentrated in one route group?
29
30**3. Write `SEO_AUDIT.md`** to repo root. Findings ranked by **traffic-impact × fix-effort** in a quadrant — high-impact / low-effort first.
31
32**4. Open ONE PR** with the highest-confidence, low-risk fixes only: adding viewport meta, adding missing meta descriptions, adding `Sitemap:` line to `robots.txt`, adding explicit GPTBot/ClaudeBot allow-or-block stanza, adding root `Organization` JSON-LD. Leave architectural calls (CSR → SSR migration, image pipeline rework) for human decision in the audit doc.
33
34## Output format — `SEO_AUDIT.md` shape
35
36```
37# SEO Audit — example.com — 2026-04-26
38
39## Quadrant
40 LOW EFFORT HIGH EFFORT
41HIGH IMPACT | Add meta descriptions | Migrate /blog to SSR
42LOW IMPACT | Tidy llms.txt | Refactor schema graph
43
44## Findings
45
46### [P0] Sitemap not referenced in robots.txt
47Severity: high · Effort: 5 min · Confidence: 100%
48Fix: Add `Sitemap: https://example.com/sitemap.xml` to `app/robots.ts`.
49
50### [P0] LCP 4.1s on /pricing (p75 mobile)
51Severity: high · Effort: medium · Confidence: 90%
52Cause: hero image not preloaded, no priority hint.
53Fix: <Image priority fetchPriority="high" /> on hero.
54
55### [P1] No GPTBot/ClaudeBot stanza in robots.txt
56Severity: medium · Effort: 2 min · Confidence: 100%
57Decision required: allow or block? Both are valid choices.
58```
59
60## Lifecycle awareness
61
62Mirroring the lifecycle pattern in `finding-underserved-keywords`:
63
64- **Initial (pre-launch / first 3 months):** focus on indexability, schema, sitemap correctness, canonical hygiene, robots.txt sanity. Core Web Vitals data isn't statistically meaningful yet — CrUX needs traffic.
65- **Growth (3–12 months):** add CWV regressions and mobile-friendliness; cross-reference GSC index coverage to catch routes silently dropping out.
66- **Mature (12+ months):** decay defense — schema drift (types deprecated upstream at schema.org), CWV regressions from third-party script creep, sitemap bloat from old URLs, AI-crawler policy review as new bots emerge.
67
68## Common mistakes
69
70- Running the audit before the site is deployed — most checks need a live URL.
71- Conflating crawlability with rankings — fixing robots.txt won't lift a thin-content page.
72- Skipping mobile — Google indexes mobile-first; desktop-only Lighthouse misses real failures.
73- Blocking AI-search bots without realizing — broad `Disallow: /` against `User-agent: *` blocks ClaudeBot too [3].
74- Treating Lighthouse SEO score as the audit — it's 8 pass/fail checks, not a strategy [5].
75
76## Common false positives
77
78- Lighthouse flagging "image elements do not have explicit width and height" on the LCP image when it's *intentionally* the hero — that's correct architecture, not a bug.
79- Schema.org validator "warnings" that are recommendations, not errors — distinguish before opening a PR.
80- PSI showing CWV "needs improvement" on a brand-new page — CrUX field data is sparse; lab data only at this stage.
81- `llms.txt` missing — flag as suggestion only; no measurable AI-citation effect yet [8].
82
83Citations and verification tags in [SOURCES.md](SOURCES.md).
aibot88